The present invention relates to a method for manufacturing biodegradable molded articles which can be decomposed by microbes, bacteria, etc., in the soil.
Generally, plastics are used as materials for molded articles such as containers, packaging materials, etc. However, plastics have the following disadvantages which give rise to problems in their waste treatment after use. In such molded articles the biodegradability thereof is extremely low and sometimes even a toxic gas is generated when incinerated. Thus, the difficulties in the waste disposal (burying, incinerating, compositing, etc.,) of the plastics create serious social problems.
In place of the described molded articles made from plastics, recently biodegradable molded articles have been used which can be decomposed by microbes, bacteria, etc., in the soil. As described, since the biodegradable molded articles can be easily decomposed in the soil, the problem associated with the waste disposal of the conventional molded articles made from plastics can be eliminated. Moreover, such biodegradable molded articles are safe to use as containers for foods.
Conventionally, the described biodegradable molded articles are manufactured by placing a biodegradable raw material in a mold heated beforehand to a predetermined temperature, and with an application of conventional thermal conductive heating. Alternatively, the biodegradable molded articles may be formed in any shapes as desired with an application of pressure by means of a high pressure press.
However, the above-noted conventional heating process creates the following problems.
1) From the heated mold, heat is dissipated not only to the materials placed in the mold, to be heated, but also into the area surrounding the mold, thereby presenting the problem of poor energy efficiency. PA1 2) Furthermore, because of this excess heat dissipation, the temperature of the area surrounding the manufacturing device increases, thereby resulting in unfavorable working conditions; and PA1 3) Since a long time is required for entirely transferring heat to the materials to be molded placed in the mold, it is difficult to complete the process in a short time, thereby resulting in low productivity. PA1 4) In order to complete the process in a short time, if the mold heated beforehand to a higher temperature is used, a great difference in temperature arises between the surface portion of the molded article and the inside portion of the molded article, thereby presenting the problem of non-homogeneous structure of the resulting molded article; and PA1 5) Since the mold must be heated to a predetermined temperature beforehand, excess energy as well as time is required. PA1 1) The device itself becomes larger in size, and the production facilities of large scale are required; PA1 2) Large noise and great vibrations occur in the manufacturing process, thereby presenting the problem of unfavorable working conditions; and PA1 3) Since the method requires the generation of high pressure, it is necessary to be cautious during the dangerous operation.
Meantime, the method to be preformed under an applied pressure by means of the high-pressure press creates the following problems.